1. Field of the Invention
The present invention relates to methods of fabricating precision aligning surfaces on discrete devices such as, for example, ink jet printheads, and more specifically to methods of fabricating ink jet printheads which can be butted against an aligning substrate to form an extended staggered array printhead.
2. Description of Related Art
Thermal ink jet printheads typically include a heater plate which includes a plurality of resistive heating elements (heater elements) and passivated addressing electrodes formed on an upper surface thereof and a channel plate having a plurality of channels, which correspond in number and position to the heating elements, formed on a base surface thereof. The upper surface of the heater plate is bonded to the base surface of the channel plate so that a heater element is located in each channel. The channel plate usually includes at least one fill hole extending from its upper surface to its base surface which is in direct fluid communication with the channels so that ink is supplied from a source into the channels.
Discrete printheads may be fabricated by forming a plurality of sets of heating elements and a plurality of sets of channels in separate (100) silicon wafers which are later bonded to each other and separated, such as by dicing, to form discrete printhead modules. The sets of heater elements and sets of channels are located on their respective silicon wafers in a plurality of rows and columns to form corresponding matrices thereon. The bonded wafers are separated between each row and column to form the discrete printhead modules. Each discrete printhead module includes a portion of the wafer containing the heater elements (known as a heater plate) and a portion of the other wafer containing a set of channels (known as a channel plate). After forming the discrete printhead modules, a plurality of the printhead modules can be aligned and butted against one another on a support substrate, such as a heat sink, to form a pagewidth printhead formed from a linear array of printhead modules. See, for example, FIG. 3D of U.S. Pat. No. 5,000,811 to Campanelli, the disclosure of which is incorporated herein by reference. Alternatively, the pagewidth printhead can have discrete printhead modules staggered on both sides of the support substrate. See, for example, FIG. 17 of U.S. Pat. No. 4,463,359 to Ayata et al, the disclosure of which is staggered array, the discrete printhead modules are aligned on the support substrate by butting each module against an aligning member of an aligning substrate and then bonding the aligned modules to the support substrate.
A critical part of the assembly lies in the precise butting of adjacent modules (of a linear array), or of modules against the aligning member (for a staggered array). This can only be accomplished if a precision butting (or aligning) surface is provided on the modules. Such precision is made difficult since the printhead modules comprise a plurality of components (e.g., channels or heater elements) closely spaced thereon. In order to ensure that the components of each module are aligned with each other, the butting surfaces of the modules must be located as precisely as possible relative to the end components on the plates.
FIG. 1A shows a butting edge of a printhead module formed by a single through cut. A first wafer 10 containing a plurality of sets of channels on one surface thereof is bonded to a heater element containing surface of a second wafer 12. A dicing blade 100 is then used to cut through the bonded wafers 10 and 12 to define side edges of discrete printhead modules 13. FIG. 1A shows the source of errors associated with the single pass dicing cut. The dicing blade 100 cuts a V-groove creating a beveled edge with a variable angle .theta.. The angle .theta. generated by the dicing blade 100 causes cut placement error from module to module, and more importantly from wafer to wafer due to the non-vertical nature of the through-cut. The angle .theta. error is caused by: depth of cut, cooling (the blade is cooled with water--if one side of the blade is cooled more than the other, thermal expansion will cause the blade to bend), blade wear on the side of the blade, and blade fatigue (i.e., blade stiffness loss due to thermal and mechanical stress). The error caused by angle increases with blade exposure (i.e., the distance blade 100 extends beyond supporting flange 102). The deeper the cut, the more blade exposure is required.
The individual printhead modules 13 formed by this method are aligned on an alignment substrate 15 and then bonded to a support substrate, such as a heat sink 17 to form a staggered array printhead. Printhead modules are usually bonded to both sides of support substrate 17 in staggered form. As shown in FIG. 1B, the printhead modules are aligned in one direction on alignment substrate 15 by butting one of their beveled side edges against a corresponding aligning member 50. Preferably, the aligning member is sized so that it will contact the printhead module 13 close to the component surface thereof (the electronic surface of the heater plate and the channel surface of the channel plate). Aligning errors between each printhead module and aligning member are introduced because: a) the alignment surface of the printhead module (the component surface of each plate) corresponds to an area of the dicing blade which is not well supported (this portion of the dicing blade is located far from flange 102); and b) misalignments between the channel plate and heater plate are transferred to the butting operation if the aligning member abuts the heater plate.
U.S. Pat. No. 5,000,811 to Campanelli discloses a method of fabricating a buttable edge surface in a substrate comprising sawing at least one backcut in a base surface of the substrate with a standard dicing blade and cutting at least one precision through cut on an upper surface of the substrate with a resinoid dicing blade corresponding to the backcut to form a buttable surface for the substrate. The method in particular is directed toward a method of fabricating a buttable aligning surface for an ink jet printhead module consisting of a heater plate and a channel plate. After a heater-element-containing-substrate and a channel-containing-substrate have been bonded together, a backcut is made on a back side of the heater-element-containing-substrate. The backside of the heater-element-containing-substrate is the adhesively mounted to a support surface. A precision through cut, aligned with the backcut, is then made from a top side of the channel-containing-substrate to cut through the channel and heater substrates without cutting into the support surface. The backcut reduces the length of a vertical butting surface formed on the resulting printheads and eliminates a non-linear portion of the through cut. One drawback of this method is that the buttable-surface defining cut (the precision through cut) cannot be visually aligned with the channels because the channels are located between the bonded substrates. Another drawback is that cuts must be formed in both sides of the bonded substrate pair, increasing handling of the substrates (i.e., a flipping step is required, and the flipped bonded substrate pair must then be realigned to a dicing jig).
U.S. Pat. No. 4,878,992 to Campanelli discloses a method of fabricating thermal ink jet printheads from two mated substrates (channel wafer/heater wafer) by two dicing operations. One dicing operation cuts completely through the channel wafer and produces a nozzle face by using a resin based blade having a predetermined thickness and diameter. After the first cut, a second cut is made by a standard blade which may have a smaller thickness. The second cut is directed into a groove made by the first cut and completely severs the bonded substrate (including heater plate wafer) into rows of printheads. The second dicing blade is then used to cut the individual rows of printheads into individual printheads. The use of the resin based blade for the first cut provides an improved nozzle face surface.
Japanese Laid-Open Patent Application No. 58-52846 discloses a semiconductor device which is formed by two step dicing. The semiconductor device includes an insulating substrate which is adhered to a supporting substrate. A multi-layered structure substrate is formed by adhering a silicon (Si) substrate on a surface of the insulating substrate. A first dicing step using a first dicing blade forms a groove a prescribed depth into the Si substrate. A second dicing step using a second blade having a width narrower than the first dicing blade is used to cut the remaining part of the Si substrate, the insulating substrate and a part of the supporting substrate.
Japanese Laid Open Patent Application No. 60-157236 discloses a dicing method for a semiconductor in which an adhesion sheet is adhered to a back of a semiconductor substrate where a circuit has been formed. The semiconductor is fully cut or half-cut by a dicing saw. Thereafter, the adhesion sheet is adhered to the front of the semiconductor substrate. The semiconductor substrate is then cut a portion of the substrate thickness by a second saw which is wider than the first.
U.K. Patent Application No. 2,025,107 discloses a method for manufacturing liquid crystal display elements. A pair of glass substrates are spaced and heat bonded to form a plurality of cells. Each cell contains regions in which electrodes are formed. U-section grooves are cut between the regions on an electrode bearing side of the substrates while corresponding linear scratches are made on opposite sides of the substrates. Splitting into individual units is performed by bending the substrates across parallel supports.
Other patents of interest include: U.S. Pat. No. 4,786,357 to Campanelli et al; U.S. Pat. No. 4,814,296 to Jedlicka et al; U.S. Pat. No. 4,829,324 to Drake et al; and U.S. Pat. No. 4,851,371 to Fisher et al. These patents relate generally to the fabrication of semiconductor devices, and particularly to the fabrication of ROS devices such as ink jet printheads and RIS devices such as image sensors. These patents can be referred to for a more detailed description of conventional processes used in the fabrication of semiconductor devices such as standard and precision dicing techniques as well as channel and heater element forming techniques. The disclosures of these patents are incorporated herein by reference.
Another method is known which produces printhead modules whose lateral butting area is minimized to avoid non-vertical standoff. This method requires three separate dice cuts, as shown in FIGS. 2A-C. A channel plate wafer 10 and a heater plate wafer 12 are bonded together to form a sandwich 14. The sandwich 14 is diced from the top by a first clearance cut 16, followed by a precision cut 18, then followed by a cut 20 from a bottom of the heater plate wafer 12 to produce printhead modules 13 having buttable edges 24. The printhead modules 13 can then be butted against an aligning member 50 on an alignment fixture 15 (see FIG. 3A) to form a staggered array. Alignment fixture 15 includes a lower planar substrate, an extended planar front wall 51, and a plurality of planar aligning members 50. The front wall 51 and the plurality of members 50 define a plurality of recesses into which a corresponding printhead module 13 is placed. The buttable edge 24 on one side of each module is butted against one side of member 50 to align that module in one direction. The nozzle-containing surface of each printhead module is butted against front wall 51 to align all of the modules in another, perpendicular direction (the nozzles of each printhead are shown in FIG. 3A for clarity, however it is understood that the nozzles would face in the opposite direction from what is shown, i.e., toward front wall 51). For more details of this alignment substrate and method for forming a staggered array, see FIG. 7 of U.S. patent application Ser. No. 07/542,053, filed Jun. 22, 1990, now U.S. Pat. No. 5,065,170, by Ivan Rezanka et al, and entitled "An Ink Jet Printer Having a Staggered Array Printhead". Alternatively, adjacent printhead modules could be butted against each other to form a linear array as shown in FIG. 3B. The printhead modules 13 are bonded to a support substrate 17, such as, for example, a heat sink, using adhesive 19.
One drawback of this process is that the last cut 20 requires flipping the wafer over during manufacture. This step is disadvantageous due to the added time required to perform the flipping operation which increases production costs and reduces production rates. Additionally, as with the example of FIGS. 1A-B, the portion of the dicing blade which forms the butting surface on each module is located far from the blade support.
It is desirable to form lateral aligning surfaces on semiconductor devices having a minimum height to avoid the above discussed non-vertical standoff problem. Minimizing the height of the aligning surface reduces lateral standoff which occurs due to any non-vertical portions of the aligning surfaces. For a further description of non-vertical standoff, see FIGS. 1-4 of U.S. Pat. No. 4,851,371.
It is also desirable to use a precision dice cut to define the aligning surface. However, since precision cutting blades (which are preferably used when forming precision dice cuts) are expensive and bend when forming deeper cuts, it is desirable to minimize the depth of any cut made with a precision cutting blade. This increases the useful life of the precision cutting blade and reduces the amount of bending which occurs in the blade when cutting.